1. Field of the Invention
The present invention relates to a light source device for a three-dimensional display which rapidly turns on a small number of LEDs to present a stereoscopic image to an observer in a wide range of viewing angles even if the observer moves sideways or the image is viewed by two or more observers from multiple visual points. More particularly, the invention relates to a light source device for three-dimensional display that has an image display means for creating an image using transmitted light.
2. Description of the Related Art
A technology for visualizing an object in three dimensions has been under development and studies on a method of displaying a three-dimensional image have been conducted in many fields, with a variety of techniques already put to practical use. There are two types of three-dimensional visualization systems. One type requires an observer to wear a device such as special eyeglasses or goggles and the other uses no special device on the observer.
The first system (eyeglass type) includes a so-called anaglyph system, in which a viewer wears a pair of eyeglasses, one attached with a red filter and the other with a blue filter; and a polarized eyeglass system, which uses a pair of eyeglasses attached with polarizing filters that transmit linearly polarized light and whose transmission axes are set perpendicular to each other. In these systems a viewer sees with his two eyes disparate images of an object that produce a binocular parallax so that the viewer can see a generally stereoscopic view. However, with these systems the viewer needs to wear cumbersome special eyeglasses.
Among proposed stereoscopic display systems that do not use the special eyeglasses are a parallax barrier system and a lenticular system.
Japanese Patent Disclosure No. 10-63199 discloses a stereoscopic imaging system in which, as shown in FIG. 4, a right-eye polarizing filter portion 66a and a left-eye polarizing filter portion 66b with their respective polarizing axes set perpendicular to each other are arranged on the left- and right-side areas of a light emitting surface of a two-dimensional or 2D light source 65; in which rays of light that have passed through the filter portions 66a, 66b are collimated by a Fresnel lens 63 into parallel rays that are then projected onto a liquid crystal device 62; and in which the liquid crystal device 62 has on both surfaces thereof linear polarizing filters 621, 622 each comprising horizontal lines of filters La, Lb having their polarizing axes set perpendicular to each other, with the horizontal filter lines La, Lb alternated in the vertical direction. In this example, the opposing linear polarizing filter lines, one on the light source 65 side and the other on the viewer side, are set such that their respective polarizing axes are perpendicular to each other. A liquid crystal panel 620 of the liquid crystal device 62 has an image formed thereon so that image information for the right eye and image information for the left eye are arranged along the horizontal filter lines of the two opposite polarizing filters and alternated in the vertical direction, permitting either of the items of image information to appear every other horizontal line.
In any of the systems described above—the binocular parallax barrier system, the lenticular system and the system disclosed in Japanese Patent Disclosure No. 10-63199—because the stereoscopic viewing range is limited, if the observer's position is shifted left or right even slightly, the stereoscopic image is inverted left or right, or if it is a case of the invention published in Japanese Patent Disclosure No. 10-63199, only a 2D image is displayed. Another problem with this system is that an image can only be presented to a single observer. To deal with these problems, a method (for example, Japanese Patent Disclosure No. 8-262370) has been proposed which involves measuring the position of an observer and mechanically moving the light source (as indicated by an arrow A in FIG. 4) according to the observer's movement. This method, however, is not practical because of its slow response speed and because a mechanical driving device easily wears out and lacks sufficient durability. Further, when an on observer shifts sideways, he or she cannot see the intended stereoscopic image.
Further, in a case where a 2D image signal is received, even if the images for the left and right eyes are displayed at the same time on a three-dimensional display which cannot display the 2D image, when the position of an observer shifts left or right even slightly, the two images reaching the left and right eyes have half an original vertical resolution of the liquid crystal device because both the left and right eyes receive both the left- and right-eye 2D images.
The present invention has been accomplished to overcome these problems. A first object of the present invention is to provide a highly precise and durable light source device for three-dimensional display which does not use a mechanical construction and thus can rapidly move an illuminating point on a light source to a position that best matches the positional movement of an observer. In this invention, a control to move the position of an illuminating point on a light source is referred to as a turn-on control.
A second object of this invention is to provide a light source device for three-dimensional display which can turn a light source on and off at a speed high enough to allow the light source to be turned off during a synchronization signal and blanking periods to eliminate unwanted afterimages and interferences and to reduce power consumptions significantly. In this invention, a control for turning off the light source during the synchronization signal and blanking periods is referred to as a turn-off control.
A third object of this invention is to provide a light source device for three-dimensional display which, when used on a time-division type three-dimensional display, can obviate the use of a shutter device in a light source thus simplifying the construction and eliminating a light transmission loss.
A fourth object of this invention is to provide a light source device for three-dimensional display which, with a limited number of LEDs as a light source, can form a wide viewing angle image on a two- or three-dimensional display. In this case, by using a known eye position tracking device, such as an ultrasonic tracking device, infrared tracking device or image tracking device, it is possible to present a stereoscopic image to an observer even if eyes of the observer move or the display is viewed by two or more observers.
A fifth object of this invention is to provide a light source device for three-dimensional display which can easily display a 2D image signal at an increased resolution because it is desired that the three-dimensional display can display a 2D image.